Cellular telephone communications have in recent years become extremely popular in the United States and other parts of the world. The Federal Communication Commission (FCC) originally allocated specific frequencies for transmission and reception of such cellular communications. Due to the success and popularity of such cellular communication, the FCC later allocated additional frequencies in order to make more channels available. Due to the need for maintaining compatibility with the originally allocated frequencies of 870-890 megahertz (mhz) for transmission and 825-845 mhz for reception and the sub-bands therein allocated between non-wireline service and wireline service, these additional frequencies were allocated relatively narrow bandwidths for both non-wireline and wireline service.
As a result of this increase in bandwidth and the resulting addition of two additional sub-bands for reception and transmission, a means for filtering unwanted frequencies for both the non-wireline and wireline services became critical. In particular with regard to the wireline service, an additional non-wireline 1.5 mhz sub-band which lies between the two wireline sub-bands must be effectively attenuated for wireline reception.
As set forth in the present assignee's U.S. Pat. 4,862,122, dielectric notch filters have been developed that have the desired characteristics of presenting a relatively low impedance having a primarily resistive characteristic within a fairly narrow bandwidth of frequencies while maintaining a relatively small physical size in comparison to other filters. Such a dielectric notch filter also has a high quality factor (Q) so as to present little attenuation outside of the desired frequencies. The specific details associated with the dielectric notch resonators used in such filters is set forth in the present assignee's U.S. Pat. No. 4,896,125, entitled Dielectric Notch Resonator. Such prior art resonators and dielectric notch filters found therefrom have achieved the desired results of narrow bandwidth and relatively small physical size while operating in the UHF frequency range.
The present invention sets forth a new resonant cavity design and the resulting dielectric notch resonators and dielectric notch filters that can be formed therefrom.
In particular, the present invention results in a resonant cavity formed in an integrated modular fashion. These cavities form the housings for dielectric notch resonators, which in turn can be coupled to form a dielectric notch filter. In particular, the individual resonant cavities can share common walls by means of divider closure plates which are dimensioned to interfit with the interior perimeter of a shell forming the remaining portion of the resonant cavity. This design reduces the materials necessary for forming the individual cavities as well as the physical space which otherwise would be necessary if duplication of parts were required. Furthermore, because of the modular design of each resonant cavity, the cavities can be stacked together to form a single multi-cavity housing forming part of an overall dielectric notch filter. Due to the closeness of the cavities to one another, electrical losses associated with a coupling transmission line are reduced as compared to such prior art multi-resonant cavity dielectric notch filters.
The overall result is a modular resonant cavity and dielectric notch resonator and filter formed therefrom which exhibit desired high frequency attenuation characteristics. The modular dielectric notch filters are particularly suited for cellular communication applications. The modular design of the resonant cavities reduces materials and labor costs and also allows for easy modification of the desired characteristics of the associated dielectric notch filter by changing the size of the resonant cavity shell.